The Hidden Photos Within Photos

It’s well known that digital photos, like PDF files and Word docs, can contain meta data that leak information the publisher didn’t intend to reveal. Less acknowledged is that some cameras also embed a small thumbnail image of the original photo that can survive subsequent tinkering and cropping — allowing a before-and-after comparison.

Hacker Tonu Samuel has put together a nifty demonstration of this on his Estonia-based website. He’s written a web crawler that’s scouring the internet for images with hidden thumbnails, and displaying both the final image and the uncensored thumbnail to a waiting world.

Most of the photo manipulation exposed on his site is simple reorientation or minor tweaking. Some of it, though, is revelatory, like the image of a topless sunbather that had been cropped to hide additional tanners on either side. Or the redacted document found on the FBI’s website, with an unredacted (but too small to read) thumbnail embedded within.

Making this all possible is the Exchangeable Image File (EXIF) digital photo standard, which adds fields for a timestamp and the camera’s make and model, among other things. Windows and OS X automatically reveal some of this data, and there’s plenty of freeware on the web for checking out the thumbnails yourself.